Heat exchangers that are designed to heat physiological solutions at relatively high solution flow rates, e.g. greater than about 60 ml/min., are known. For example, see my earlier U.S. Pat. No. 4,759,749 where a heat exchanger having an inner tube that carries a warming fluid and an outer tube that forms a channel for the solution to be warmed is described. It is also known to provide a heat exchanger for maintaining the temperature of a physiological solution that is flowing at a substantially lower rate. For example, see my earlier U.S. Pat. No. 5,063,994 where a heat exchanger having a central tube for carrying the solution to be warmed and outer channels for carrying the warming fluid is described.
Heat exchangers such as those described above have been designed to be operated as separate units. That is, each heat exchanger has fluid heating characteristics for particular uses, and each has its own, independent source of warming fluid. While the heat exchangers can be used simultaneously for the same patient, such use is awkward, at best, because of the duplication of various parts, particularly the pumps and reservoirs for the warming fluids. This often means that the physician chooses to use only one of the units, which leads to the patient's receiving (1) heated solutions too slowly, as when the unit having a lower flow rate capability is used even though it is too small, or (2) solutions that are at lower than optimum temperature, as when the unit having a higher flow rate capability is operated at a rate that is too low to maintain temperature in the line to the patient.